Oil well cementing and other underground cementing operations often require placement of a cement slurry in a porous environment such as porous earthen or rock strata.
Problems develop when water filters out of the slurry into the porous media during the setting period. As a result of the rapid water loss, the cement acquires impaired qualities of strength and an uncontrollable setting rate. Also, the water loss from the cement frequently damages the surrounding strata formation. The problem is not cured by producing a cement slurry containing more water. This results in serious placing and setting problems.
Additives have been used to control fluid loss from cement in a porous environment with varying success. For example, U.S. Pat. No. 3,140,269 to Wahl et al. discloses additions of a combination of a copolymer of maleic anhydride and an N-vinyl nitrogen-containing ring monomer, a poly (aryl-vinylbenzyl) compound, and water to Portland or aluminous cement. U.S. Pat. No. 3,662,830 to Martin discloses admixing a salt of lignosulfonic acid and boric acid or a borate with a cement slurry. Other fluid loss additives include carboxymethyl hydroxyethyl cellulose and bentonite. However, these additives are usually accompanied by one or more undesirable effects such as retardation of the setting rate, incompatability of the additive with other cement additives present, precipitation of the cement prior to set, and lessening of the ultimate physical properties of the set cement. Also, economic scarcity and high cost have made many of the additives impractical.
An effective fluid loss control additive exhibiting the most desirable qualities has been the polyamines. Their use is well known. U.S. Pat. No. 3,491,049 to Gibson et al. discloses an aqueous hydraulic cement slurry including hydraulic cement, water, a surfactant, and a small amount of polyalkylenepolyamine, polyalkylenimine or a mixture thereof. McKenzie et al. discuss use of liquid polyamines with lignosulfonate in their article entitled "Polyamine Compounds Control Cement Fluid Loss in Freshwater or Seawater Slurries", Oil & Gas Journal, Mar. 29, 1982, pp. 146-148.
Use of polyamines as an additive has some serious drawbacks however. The polyamines are available only as liquids, usually as 30-50 percent active solutions of the polymers in water. Consequently, they can be added to the hydraulic cement only at the time of formation of the cement slurry. This must be done at the well site immediately prior to pumping the slurry into the well. Under these circumstances, the liquid polyamines must be available at the well and measured for mixing with the cement under non-ideal conditions.
The liquid polyamines also require addition of sulfonated polymers to the cement composition to provide effective fluid loss control. It has been known that sulfonated polymers form a slimy pultaceous precipitate with the polyamines. This is disclosed in U.S. Pat. No. 2,839,417 to Tousignant et al. This precipitate is the effective fluid loss control agent. The sulfonated polymers have the characteristic of acting as retardants. This characteristic is undesirable at temperatures below 100.degree. F.
For the above stated reasons, it is highly desirable to have a solid particulate composition having the superior fluid loss control qualities of the polyamines. This composition could be pre-mixed with dry hydraulic cement obviating the need to add any liquids other than water to create the cement slurry. Also, the amount of additive to be mixed with the hydraulic cement could be measured in a highly controlled area away from the well site. Further, it would be desirable to have a polyamine fluid loss control additive that would be effective at temperatures below 100.degree. F. without sulfonated polymers.